Summary of Changes in Estimated Fair Value (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
Sep. 30, 2013
Fair Value Inputs Assets Quantitative Information [Line Items]
Balance as of December 31, 2012	$ 683
Recognized gain upon final remeasurement	(24)
Reclassification of warrant liability to additional paid-in capital	(659)
Balance as of September 30, 2013

Reclassification of warrants liability to additional paid in capital.

No definition available.

Name:	ptla_ReclassificationOfWarrantLiabilityToAdditionalPaidInCapital
Namespace Prefix:	ptla_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration